Abstract: The minimum lethal concentration, mortality, semi-lethal concentration (LC50) and safe concentration of some chemical disinfectants were studied for Japanese flounder (Paralichthys olivaceus) larvae.The susceptibility of the juvenile Japanese flounder to six chemical disinfectants was as follows: malachite green > sodium chlorite > chlorine dioxide > No 1 disinfectants > cupric sulphate > potassium permanganate. Yet, use of disinfectants were discussed for prophylactic treatments and therapeutic treatments of diseases.